Packets and Protocols on a Network · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Packets and communication rules

Computing · Computer Systems · ages 15-16
Name ______________________   Date ____________

  1. What do TCP sequence numbers help a receiver do?

    • Put received data into byte order
    • Identify the complete route taken by each received packet
    • Treat arrival order as the original order without checking

  2. How can splitting a large transfer into packets help users share a link?

    • It reserves the link for that transfer until every packet arrives
    • It gives each packet a private physical cable for its whole journey
    • Other users' packets can travel between its packets

  3. Packets sometimes arrive out of order.

    Circle one:   True   False

  4. A TCP receiver has all bytes through 36 and none after 36. It next receives bytes 73-90. What can it conclude?

    • Bytes 37-72 have not arrived yet
    • Bytes 37-72 were definitely destroyed on the network
    • Bytes 37-72 are unnecessary because later data arrived

  5. TCP has unacknowledged data and its retransmission timer expires. What does it do?

    • Treat the timeout as acknowledgement that the data arrived
    • Retransmit the unacknowledged data
    • Wait indefinitely because only the receiver can request a retry

  6. What is a network protocol?

    • The physical route followed by one particular packet
    • Agreed rules for exchanging data
    • Permission for every device to join any available network

  7. An email transfer needs complete, ordered data. A game's frequent updates can skip old updates. Which transport choice fits those needs?

    • UDP for email; TCP for the game's replaceable updates
    • TCP for email; UDP for those game updates
    • UDP for both because UDP automatically resends every missing update

  8. Some data for a compressed video frame is missing. Why might a call continue but show unclear blocks?

    • Every missing byte must arrive before any part of the call continues
    • The unclear blocks prove every packet for the call has been lost
    • Other data can arrive while part of the image lacks information
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Packets and communication rules W1-mt_IffXVDtfLX-s1

  1. Put received data into byte order · Sequence numbers identify byte positions. They help restore data order when arrival order differs.
  2. Other users' packets can travel between its packets · Smaller packets allow traffic from several users to share a link. Packet splitting alone does not guarantee fair sharing.
  3. True · Arrival order can differ from sending order.
  4. Bytes 37-72 have not arrived yet · Under the stated receipt conditions, bytes 37-72 remain missing. They could be delayed or lost.
  5. Retransmit the unacknowledged data · The timeout triggers retransmission. It does not establish that the original data was lost or received.
  6. Agreed rules for exchanging data · Protocols define communication rules. They are not individual routes or grants of network access.
  7. TCP for email; UDP for those game updates · TCP supplies reliable ordered transport. UDP can suit the stated replaceable updates, with the application handling its recovery needs.
  8. Other data can arrive while part of the image lacks information · Some missing frame data can affect image regions while other data arrives. The appearance alone would not prove packet loss.
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